Study of tungsten oxidation in O2∕H2∕N2 downstream plasma

Abstract

The surface oxidation of tungsten is a serious issue in plasma processing of advanced integrated-circuit devices where tungsten is being used as a gate electrode. In this article, we study tungsten oxidation in O2∕H2∕N2 downstream plasma at a temperature ⩽300°C. The results show that oxidation occurs rapidly in O2 downstream plasma to form stable WO3. However, oxidation can be reduced effectively by adding H2 and totally suppressed when H2 concentration in the gas feed reaches a certain low level at which the plasma is still oxygen dominant. Tungsten oxidation increases significantly with sample temperature and exposure time in O2 downstream plasma. However, H2 addition reduces both temperature and time dependences due to the coexistence and competition of oxidation and reduction processes. When N2 is also added, the efficiency of H2 in O2 downstream plasma in controlling tungsten oxidation is lowered. The findings may provide effective approaches to various applications of selective oxidation over tungsten, such as photoresist stripping and polysilicon oxidation on tungsten gate structures.